FORT POLK, LA.
— In recent years the US military has devoted much money and effort to preparing for 21st-century urban warfare - and this preparation may be facing its fiercest test yet in the Euphrates city of Fallujah, as the initial offensive began Monday.

Fallujah's narrow streets, mosques, and ancient neighborhoods make the city an archetype of an insurgents' redoubt. Defenders will try to use their knowledge of the terrain to gain advantage over the better armed and trained Americans. US forces will likely tighten a noose around contested areas, while attacking from unexpected directions in an attempt to confuse the enemy.

In the long run, the central question may be whether physical control of Fallujah equates to its eventual pacification. In the short run, there's little doubt that US forces will eventually gain control of the city, say military officials and outside experts. New training, tactics, and equipment - plus the weight of American firepower - will see to that.

US commanders hope Fallujah will prove an opportunity to weaken the insurgency, but they don't count on it. Fallujah "has the potential of being a very intense fight, even for a matter of weeks, but I don't think it's a center of gravity," says Maj. Gen. William Webster, commander of the 3rd Infantry Division, whose forces are undergoing a final urban-training exercise at Fort Polk, in preparation for deployment to Iraq. It would be a center of gravity only if the enemy concentrates there, he says.

In many respects, the fight for Fallujah - dubbed Operation Phantom Fury - epitomizes the urbanization of conflict in Iraq and around the world, as insurgents and terrorist groups increasingly operate concealed in sprawling population centers in a bid to survive against militarily superior government forces.

As the world's urban population has multiplied from roughly half a billion in 1950 to more than 3 billion today, while the size of the US military has fallen sharply, cities such as Fallujah are posing daunting demands on the resources of US commanders, who must carefully pick and choose where to allocate forces to "make manageable the chaos," writes Russell Glenn, an expert in urban warfare, in a 2004 RAND briefing. He likens the challenge of urban combat to the parable of blind men "visualizing the elephant."

"Moving into urban terrain is the one way our adversaries can level the playing field," says Col. Randy Gangle (Ret.), director of the Marines Corps Center for Emerging Threats and Opportunities at Quantico, Va. "It's the most complex battle space you can find yourself in, the way buildings conceal and channelize your movement and give your enemy cover, and the civilians that compact the problem."

The clutter of buildings creates unlimited fighting positions for enemy forces, while making it harder for US forces to see and communicate.

The close combat requires quick movement and decisions, even while it raises the risk of fratricide and killing innocent civilians. Historically, civilians have suffered several times the casualties of US forces in urban battles such as the cases of Hue in Vietnam in 1968, Panama in 1989, and Mogadishu in 1993.

The challenge of defeating insurgents while avoiding civilian deaths requires a far greater emphasis by US forces on intelligence gathering, sleuthing out patterns of enemy behavior, and winning over local populations, says Brig. Gen. Mike Barbero, commander of the premier US Army urban-training facility, the Joint Readiness Training Center (JRTC) at Fort Polk, La.

"Intelligence is the coin of the realm on this battlefield," says General Barbero, who served as assistant division commander of the 4th Infantry Division in Iraq until this summer. Soldiers pay a price for not acting quickly on intelligence - ideally within two hours, he says. "You have to be very agile ... because [if you are not], the meeting will be over, the guy paying for improvised explosive devices will be gone, or the guy on the cellphone will move to the next town."

Even if American troops rout the insurgents, rebels who have left can come back to sow the seeds of a fresh rebellion.

The swift evolution of urban training

Over the past two years, the Army has dramatically altered urban training at JRTC to prepare soldiers for the complexities of the counterinsurgency in Iraq.

The number of mock villages in the base's expanse of woods and swamps has been increased from four to 18, while 200 Arabic-speaking role players impersonating Iraqi tribesmen, police, and civilians have replaced many of the Louisiana locals.

"Before, the role players were all local guys with Southern accents who would say 'You ran over my goat'; now you go into a Kurdish village, and the mayor is from northern Iraq," says Barbero.

At the same time, US troops are undergoing urban-warfare training for longer periods in greater numbers, with support units as well as infantry. This year, for example, 16 brigades will rotate through JRTC for month-long mission rehearsals, compared with 10 brigades last year, Barbero says.

New enemy tactics used in Iraq are tracked daily, and immediately incorporated into training scenarios here. Moreover, training anticipates the specific priorities that units will face in Iraq. For example, a brigade from the 3rd Infantry Division currently at JRTC preparing to deploy to Iraq is supporting elections in various mock villages and conducting operations together with local security forces - just as it will in Iraq.

In Fallujah and in Iraq overall, the US faces one of its toughest urban toughest urban foes yet, commanders say. It is composed of highly unpredictable, loosely networked, and chaotic groups of fighters who come together to strike and then disperse. They also quickly spread lessons on the Internet.

"It is very different and very difficult, beyond what we've ever had to do," General Webster says. "This puts infinitely more demand on our young soldiers and leaders, because in urban operations you have to be very decentralized."